Duncan MacLaren Young SommervilleFRSEFRAS (1879–1934) was a Scottish mathematician and astronomer. He compiled a bibliography on non-Euclidean geometry and also wrote a leading textbook in that field. He also wrote Introduction to the Geometry of N Dimensions, advancing the study of polytopes. He was a co-founder and the first secretary of the New Zealand Astronomical Society.

Sommerville was also an accomplished watercolourist, producing a series of works of the New Zealand landscape.

The family returned home to Scotland, where Duncan first spent 4 years at a private school in Perth, before being sent to Perth Academy. He then studied at the University of St Andrews in Fife, where in 1905 he was awarded Doctor of Science for his thesis, Networks of the Plane in Absolute Geometry. Sommerville taught at St. Andrews from 1902 to 1914.

Sommerville used geometry to describe the voting theory of a preferential ballot.[9] He addressed Nanson's method where n candidates are ordered by voters into a sequence of preferences. Sommerville shows that the outcomes lie in n ! simplexes that cover the surface of an n − 2 dimensional spherical space.